1. Field of the Invention
The present invention relates to a stator for use in rotational electric machines such as electric motors and generators, an insulating bobbin for the stator and a manufacturing method of the stator.
2. Description of the Related Art
Windings for stators include a winding made up of so-called round wire having a circular cross section and a winding made up of so-called rectangular wire having a substantially rectangular cross section.
While the round wire produces a space therebetween even when the wire is wound tightly, the rectangular wire is advantageous over the round wire in that the former can be aligned so as not to produce any space therebetween whereby the space factor can be improved. When used herein, the space factor means a ratio between the cross-sectional area of the slot and an area occupied by the coil wire, and an increase in space factor increase the performance of the rotational electric machine.
The winding formed by winding the rectangular wire is disclosed, for example, in a Japanese Patent Unexamined Publication JP-A-2000-245092.
When forming a stator winding by winding a rectangular wire in an aligned fashion, however, since the surface of the stator winding so formed becomes substantially flat, when the stator winding on an outermost layer protrudes, the stator winding on the outermost layer moves in a widthwise direction, causing a risk that a desired shape cannot be maintained (refer to FIG. 28, a detailed description being provided later on).
On the other hand, Japanese Patent Unexamined Publication JP-A-2001-359250 (refer to paragraph No. 0006 and FIG. 14) proposes a technique for preventing the deviation of a rectangular wire by restricting a widthwise movement of the rectangular wire by holding portions being formed on the rectangular wire so as to protrude therefrom.
Thus, while the rectangular is advantageous in that the space factor can be increased, the rectangular becomes easy or difficult to be bent depending on a direction of its bending. So-called flat-wise bending in which the rectangular wire is bent in a thickness-wise direction thereof provides an easy bending, whereas so-called edgewise bending in which the rectangular wire is bent in a widthwise direction thereof provides a difficult bending. There may be caused a problem to introduce the rectangular wire into an insulating bobbin due to the bending properties of the rectangular wire.
FIG. 17 shows a rectangular wire introducing portion in a conventional insulating bobbin and a start-winding portion of a rectangular wire introduced. In an insulating bobbin 100, extending portions 102, 103 are provided at both ends of a tooth insulating portion being formed in a rectangular tubular shape, and an introduction support portion 104 is provided in an outer side of one 102 of the extending portions.
In a case where a rectangular wire 110 is introduced from an outside in an axial direction of the insulating bobbin 100 while a thickness-wise direction of the rectangular wire 110 is positioned so as to intersect at right angles with a plane-wise direction of a horizontal side 110a of the tooth insulating portion 101, so that the rectangular wire 110 passes through a groove 104a in the introduction support portion 104 and a groove 102a in the extending portion 102 to be wound along a vertical side 101b of the tooth insulating portion 101, the rectangular wire has to be bent at right angles in the groove 102a in the extending portion 102.
In this case, as shown in FIG. 17, when attempting to bend the rectangular wire in the groove 102a using the flat-wise bending, a twist is caused in a bent portion of the rectangular wire 110, and the bent portion that is expanded due to the twist so caused interferes with a winding of an upper layer such as a second layer or upper.
On the other hand, as shown in the same drawing, when winding the rectangular wire for an upper layer while avoiding an interference with the bent portion, a large space (a gap) where there does not exist any winding is produced as shown in FIG. 18, and hence there is caused a drawback that the space factor is decreased.
On the other hand, when bending the rectangular wire 110 in the groove 102a using the edgewise bending, such a bending cannot be implemented with a common winding machine, and therefore, a winding machine having a special construction is required, which increases the production costs. In addition, when using the edgewise bending, since the radius of curvature of the bent portion becomes smaller, there may also be caused a risk that the insulating layer of the winding is damaged.
Also, In the aforesaid conventional technique, since the holding portions are formed on the rectangular wire, a special shape is required which is different from conventional ones, and this calls for a complicated rectangular wire forming process. In addition, since the size of the rectangular wire is increased due to the provision of the holding portion, there is caused a problem that a decrease in space factor is called for.